Make sure that you have npm installed in your environment, and install the Expo client with npm install -g expo-cli. Additionally, run an npm install to install the rest of the node modules. Next, you should be able to simply npm start in the project directory, wait for the dev console to open in your web browser, scan the QR code with your phone (with the Expo app), and use the app.
config/config.js contains a number of configuration values, the most important of which to setting up your environment is USE_LOCAL_BACKEND. If this is set to true, the app will attempt to connect to an mhacks-web backend running on the same IP as Expo; if false, it will hit the live MHacks API. When just testing how the app receives information consider setting this to false, however when experimenting with changing values this should probably stay on true to stay safe.
Additionally, developer builds seem to run very badly on Android, so when developing on Android it's best to keep the Expo build on production mode.